Phase-change memory device and method

ABSTRACT

In an embodiment, a device includes: a first metallization layer over a substrate, the substrate including active devices; a first bit line over the first metallization layer, the first bit line connected to first interconnects of the first metallization layer, the first bit line extending in a first direction, the first direction parallel to gates of the active devices; a first phase-change random access memory (PCRAM) cell over the first bit line; a word line over the first PCRAM cell, the word line extending in a second direction, the second direction perpendicular to the gates of the active devices; and a second metallization layer over the word line, the word line connected to second interconnects of the second metallization layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.63/001,944, filed on Mar. 30, 2020, which application is herebyincorporated herein by reference.

BACKGROUND

Semiconductor memories are used in integrated circuits for electronicapplications, including radios, televisions, cell phones, and personalcomputing devices, as examples. One type of semiconductor memory isphase-change random access memory (PCRAM), which involves storing valuesin phase change materials, such as chalcogenide materials. Phase changematerials can be switched between an amorphous phase (in which they havea low resistivity) and a crystalline phase (in which they have a highresistivity) to indicate bit codes. A PCRAM cell typically includes aphase change material (PCM) element between two electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a block diagram of a semiconductor device, in accordance withsome embodiments.

FIG. 2 is a cross-sectional view of a semiconductor device, inaccordance with some embodiments.

FIGS. 3 through 21B are various views of intermediate stages in themanufacturing of a semiconductor device, in accordance with someembodiments.

FIG. 22 is a cross-sectional view of a semiconductor device, inaccordance with some other embodiments.

FIGS. 23A through 23E are three-dimensional views of intermediate stagesin a self-aligned patterning process for forming PCRAM cells, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, PCRAM cells are formed in aself-aligned manner with multiple patterning processes. The PCRAM cellscan thus be formed at a smaller pitch and with smaller criticaldimensions. The performance and density of the PCRAM cells may thus beimproved.

FIG. 1 is a block diagram of a semiconductor device 50, in accordancewith some embodiments. The semiconductor device 50 includes a PCRAMarray 52, a row decoder 54, and a column decoder 56. The PCRAM array 52includes PCRAM cells 58 arranged in rows and columns. The row decoder 54may be, e.g., a static CMOS decoder, a pseudo-NMOS decoder, or the like.During operation, the row decoder 54 selects desired PCRAM cells 58 in arow of the PCRAM array 52 by activating the respective word line 62 forthe row. The column decoder 56 may be, e.g., a static CMOS decoder, apseudo-NMOS decoder, or the like, and may include writer drivers, senseamplifiers, combinations thereof, or the like. During operation, thecolumn decoder 56 selects bit lines 66 for the desired PCRAM cells 58from columns of the PCRAM array 52 in the selected row, and reads datafrom or writes data to the selected PCRAM cells 58 with the bit lines66.

Although embodiments herein are described in the context of PCRAMs, itshould be appreciated that similar techniques could be applied in othermemories that use programmable resistance elements. For example, similartechniques could be used to manufacture magnetoresistive random-accessmemories (MRAMs), resistive random access memories (RRAMs), memorieswith a selector structure, and the like.

FIG. 2 is a cross-sectional view of the semiconductor device 50, inaccordance with some embodiments. FIG. 2 is a simplified view, and somefeatures of the semiconductor device 50 (discussed below) are omittedfor clarity of illustration. The semiconductor device 50 includes alogic region 50L and a memory region 50M. Memory devices (e.g., PCRAMs)are formed in the memory region 50M and logic devices (e.g., logiccircuits) are formed in the logic region 50L. For example, the PCRAMarray 52 (see FIG. 1) can be formed in the memory region 50M, and therow decoder 54 and the column decoder 56 (see FIG. 1) can be formed inthe logic region 50L. The logic region 50L may occupy most of the areaof the semiconductor device 50. For example, the logic region 50L mayoccupy from 95% to 99% of the area of the semiconductor device 50, withthe memory region 50M occupying the remaining area of the semiconductordevice 50. The memory region 50M can be disposed at an edge of the logicregion 50L, or the logic region 50L can surround the memory region 50M.

The logic region 50L and memory region 50M are formed over a samesubstrate, e.g., a semiconductor substrate 70. The semiconductorsubstrate 70 may be silicon, doped or undoped, or an active layer of asemiconductor-on-insulator (SOI) substrate. The semiconductor substrate70 may include other semiconductor materials, such as germanium; acompound semiconductor including silicon carbide, gallium arsenic,gallium phosphide, gallium nitride, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.Other substrates, such as multilayered or gradient substrates, may alsobe used.

Devices 72 are formed at the active surface of the semiconductorsubstrate 70 (e.g., the surface facing upwards in FIG. 2). The devices72 may be active devices or passive devices. For example, the electricalcomponents may be transistors, diodes, capacitors, resistors, or thelike, formed by any suitable formation method. The devices 72 areinterconnected to form the memory devices and logic devices of thesemiconductor device 50. For example, some of the devices 72 may beaccess transistors for the PCRAM cells 58.

One or more inter-layer dielectric (ILD) layer(s) 74 are formed on thesemiconductor substrate 70, and electrically conductive features, suchas contact plugs 76, are formed physically and electrically coupled tothe devices 72. The ILD layer(s) 74 may be formed of any suitabledielectric material, for example, an oxide such as silicon oxide,phosphosilicate glass (PSG), borosilicate glass (BSG), boron-dopedphosphosilicate glass (BPSG), or the like; a nitride such as siliconnitride; or the like. The ILD layer(s) may be formed by any suitabledeposition process, such as spin coating, physical vapor deposition(PVD), chemical vapor deposition (CVD), the like, or a combinationthereof. The electrically conductive features in the ILD layer(s) may beformed through any suitable process, such as deposition, damascene(e.g., single damascene, dual damascene, etc.), the like, orcombinations thereof.

An interconnect structure 78 is formed over the semiconductor substrate70, e.g., over the ILD layer(s) 74. The interconnect structure 78interconnects the devices 72 to form integrated circuits in each of thelogic region 50L and memory region 50M. The interconnect structure 78includes multiple metallization layers M1-M6. Although six metallizationlayers are illustrated, it should be appreciated that more or lessmetallization layers may be included. Each of the metallization layersM1-M6 includes metallization patterns in dielectric layers. Themetallization patterns are electrically coupled to the devices 72 of thesemiconductor substrate 70, and include, respectively, metal lines L1-L6and vias V1-V6 formed in one or more inter-metal dielectric (IMD)layers. The interconnect structure 78 may formed by a damascene process,such as a single damascene process, a dual damascene process, or thelike. In some embodiments, the contact plugs 76 are also part of themetallization patterns, such as part of the lowest layer of metal viasV1.

The PCRAM cells 58 of the PCRAM array 52 (see FIG. 1) are formed in theinterconnect structure 78. The PCRAM cells 58 can be formed in any ofthe metallization layers M1-M6, and are illustrated as being formed inan intermediate metallization layer M5. Each PCRAM cell 58 includes abottom electrode 82, a PCM element 84 on the bottom electrode 82, and atop electrode 86 on the PCM element 84. Word lines 62 extend alongrespective rows of the PCRAM cells 58 and are connected to the topelectrodes 86 of the respective rows of the PCRAM cells 58. Bit lines 66extend along respective columns of the PCRAM cells 58 and are connectedto the bottom electrodes 82 of the respective columns of the PCRAM cells58. One or more additional IMD layer(s) 88 can be formed around thePCRAM cells 58. The IMD layer(s) 88 surround and protect the componentsof the PCRAM cells 58. The resistance of a PCM element 84 isprogrammable, and can be changed between a high resistance (R_(AP)),which can signify a code such as a “1,” and a low resistance (R_(P)),which can signify a code such as a “0.” As such, a code can be writtento a PCRAM cell 58 by programming the resistance of its PCM element 84with its corresponding access transistor, and a code can be read from aPCRAM cell 58 by measuring the resistance of its PCM element 84 with itscorresponding access transistor.

The PCRAM cells 58 are electrically coupled to the devices 72. The bitlines 66 are connected to conductive features (e.g., interconnects) ofan underlying metallization pattern, such as to the metallization layerM4 in the illustrated example, by conductive vias 92. The word lines 62are connected to conductive features (e.g., interconnects) of anoverlying metallization pattern, such as to the metallization layer M6in the illustrated example, by conductive vias 94. A first subset of thedevices 72 (e.g., access transistors), such as devices of the rowdecoder 54, are electrically coupled to the word lines 62. The bit lines66 are electrically coupled to a second subset of the devices 72, suchas devices of the column decoder 56.

Referring initially to FIG. 21B, a simplified top-down view of a portionof the memory region 50M is shown. Some features of the semiconductordevice 50 (discussed in greater detail below) are omitted for clarity ofillustration. A portion of a PCRAM array is shown. As will be describedin greater detail below, the PCRAM cells 58 are formed in a checkerboardlayout. Such an array of PCRAM cells 58 is formed in a self-alignedmanner by etching a stack of conductive and phase change material (PCM)layers twice: first using a pattern of the bit lines 66, and again usinga pattern of the word lines 62. The etching processes form the wordlines 62, the bit lines 66, and the PCRAM cells 58, with each PCRAM cell58 being disposed at an intersection of a word line 62 and a bit line 66in the top-down view.

The bit lines 66 extend along a first direction D₁, which is parallel tothe active surface of the semiconductor substrate 70 (see FIG. 2) andparallel to the longitudinal axes of the gates of the devices 72 (e.g.,transistors). The bit lines 66 each emanate from a bit line pad 68. Eachbit line pad 68 is coupled to at least one bit line 66. Althoughillustrated as separate elements, as will be described in greater detailbelow, each bit line pad 68 and its corresponding bit lines 66 areactually a single continuous conductive feature. The bit line pads 68are connected to conductive features (e.g., interconnects) of anunderlying metallization pattern (such as to the metallization layer M4in the example of FIG. 2) by the conductive vias 92. As will bedescribed in greater detail below, the conductive vias 92 areelectrically coupled to the bottom electrodes 82 of the PCRAM cells 58(see FIG. 2). As such, each conductive via 92 can also be referred to asa bottom electrode via (BEVA).

The word lines 62 extend along a second direction D₂, which is parallelto the active surface of the semiconductor substrate 70 (see FIG. 2) andis perpendicular to the first direction D₁ (e.g., perpendicular to thelongitudinal axes of the gates of the devices 72 (e.g., transistors)).The word lines 62 each emanate from a word line pad 64. Each word linepad 64 is coupled to at least one word line 62. Although illustrated asseparate elements, as will be described in greater detail below, eachword line pad 64 and its corresponding word lines 62 are actually asingle continuous conductive feature. The word line pads 64 areconnected to conductive features (e.g., interconnects) of an overlyingmetallization pattern (such as to the metallization layer M6 in theexample of FIG. 2) by the conductive vias 94. As will be described ingreater detail below, the conductive vias 94 are electrically coupled tothe top electrodes 86 of the PCRAM cells 58 (see FIG. 2). As such, eachconductive via 94 can also be referred to as a top electrode via (TEVA).

FIG. 21B further illustrates several reference cross-sections.Cross-section 50C is across several PCRAM cells 58. Cross-section 50P₁is parallel to cross-section 50C, and is across a bit line pad 68.Cross-section 50P₂ is perpendicular to cross-section 50C, and is acrossa word line pad 64. Subsequent figures refer to these cross-sections forclarity.

FIGS. 3 through 21B are various views of intermediate stages in themanufacturing of the semiconductor device 50, in accordance with someembodiments. Specifically, the manufacturing of the interconnectstructure 78 (see FIG. 2) for the semiconductor device 50 is shown. Asnoted above, the interconnect structure 78 includes the PCRAM cells 58of the PCRAM array 52 (see FIG. 1).

FIGS. 3, 4, 5, 6, 7, 8, 9, 10, 11A, 12A, 13, 14, 15, 16, 17A, 18A, 19,20, and 21A are cross-sectional view illustrating the logic region 50Land the memory region 50M, including a cell region 50C (whichillustrates cross-section 50C in FIG. 21B), a first pad region 50P1(which illustrates cross-section 50P1 in FIG. 21B), and a second padregion 50P2 (which illustrates cross-section 50P2 in FIG. 21B). As willbe described in greater detail below, a bit line pad 68 (see FIG. 12A)will be formed in the first pad region 50P1, a word line pad 64 (seeFIG. 18A) will be formed in the second pad region 50P2, and the PCRAMcells 58 (see FIG. 18A) will be formed in the cell region 50C. Althoughthe first pad region 50P1, the second pad region 50P2, and the cellregion 50C are each illustrated in the same cross-sectional view, itshould be appreciated that each of the regions are in differentcross-sections, as shown by FIG. 21B.

FIGS. 11B, 12B, 17B, 18B, and 21B are top-down views illustrating thememory region 50M. FIGS. 11B, 12B, 17B, 18B, and 21B show thesemiconductor device 50 at a similar step of processing as FIGS. 11A,12A, 17A, 18A, and 21A, respectively. FIGS. 11B, 12B, 17B, 18B, and 21Bare simplified views, and some features are omitted for clarity ofillustration.

In FIG. 3, a metallization layer (e.g., M4, see FIG. 2) of theinterconnect structure is formed. The metallization layer includes anIMD layer 102 and conductive features 104 (which can correspond to themetal lines L4, see FIG. 2). The IMD layer 102 is formed over the ILDlayer(s) 74. The IMD layer 102 may be formed of any suitable dielectricmaterial, for example, an oxide such as silicon oxide, phosphosilicateglass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate glass(BPSG), or the like; a nitride such as silicon nitride; or the like. TheIMD layer 102 may be formed by any suitable deposition process, such asspin coating, PVD, chemical vapor deposition (CVD), the like, or acombination thereof. The IMD layer 102 may be a layer formed of a low-kdielectric material having a k-value lower than about 3.0. The IMD layer102 may be a layer formed of an extra-low-k (ELK) dielectric materialhaving a k-value of less than 2.5.

Conductive features 104 are formed in the IMD layer 102, and areelectrically coupled to the devices 72. In accordance with someembodiments, the conductive features 104 include diffusion barrierlayers and conductive material over the diffusion barrier layers.Openings are formed in the IMD layer 102 using, e.g., an etchingprocess. The openings expose underlying conductive features, such asunderlying metal vias. The diffusion barrier layers may be formed oftantalum nitride, tantalum, titanium nitride, titanium, cobalt-tungsten,or the like, and may be formed in the openings by a deposition processsuch as atomic layer deposition (ALD) or the like. The conductivematerial may include copper, aluminum, tungsten, silver, andcombinations thereof, or the like, and may be formed over the diffusionbarrier layers in the openings by an electro-chemical plating process,CVD, ALD, PVD, the like, or a combination thereof. In an embodiment, theconductive material is copper, and the diffusion barrier layers are thinbarrier layers that prevent the copper from diffusing into the IMD layer102. After formation of the diffusion barrier layers and the conductivematerial, excess of the diffusion barrier layers and conductive materialmay be removed by, for example, a planarization process such as achemical mechanical polish (CMP) process. In some embodiments, theconductive features 104 are metal lines (which can correspond to themetal lines L4, see FIG. 2).

An etch stop layer 106 is formed on the conductive features 104 and theIMD layer 102. The etch stop layer 106 may be formed of a dielectricmaterial such as aluminum nitride, aluminum oxide, silicon oxide,silicon nitride, silicon oxynitride, silicon carbide, a combinationthereof, or the like. The etch stop layer 106 may be formed by chemicalvapor deposition (CVD), PVD, ALD, a spin-on-dielectric process, thelike, or a combination thereof. The etch stop layer 106 may also be acomposite layer formed of a plurality of different dielectric sublayers.For example, the etch stop layer 106 may include a silicon carbidesublayer and an aluminum oxide sublayer formed on the silicon carbidesublayer. The silicon carbide sublayer can be used as a glue layer toimprove adhesion between the aluminum oxide sublayer and the IMD layer102.

An IMD layer 108 is formed on the etch stop layer 106. In someembodiments, the IMD layer 108 is formed of a tetraethyl orthosilicate(TEOS) oxide (e.g., silicon oxide deposited using, e.g., a chemicalvapor deposition (CVD) process with TEOS as a precursor). In someembodiments, the IMD layer 108 may be formed using PSG, BSG, BPSG,undoped silicate glass (USG), fluorosilicate glass (FSG), SiOCH,flowable oxide, a porous oxide, or the like, or combinations thereof.The IMD layer 108 may also be formed of a low-k dielectric material witha k value lower than about 3.0, for example. The IMD layer 108 can beformed to a thickness in the range of about 50 nm to about 150 nm.

Via openings 110 are patterned in the IMD layer 108. The via openings110 may be formed using suitable photolithography and etchingtechniques. In some embodiments, an anti-reflective layer, such as anitrogen-free anti-reflective coating (NFARC) (not shown) can be formedon the IMD layer 108 to protect the underlying layers during thepatterning of via openings 110.

In FIG. 4, conductive vias 92 are formed in the via openings 110. Theconductive vias 92 can also be referred to as BEVAs. In someembodiments, the conductive vias 92 include main conductive regions andconductive barrier layers lining sidewalls and bottom surfaces of themain conductive regions. The conductive barrier layers may be formed oftitanium, titanium nitride, tantalum, tantalum nitride, cobalt, acombination thereof, or the like. The main conductive regions may beformed of metals such as copper, aluminum, tungsten, cobalt, alloysthereof, or the like. The formation of the conductive vias 92 mayinclude conformally forming a conductive barrier layer extending intothe via openings 110, depositing a metallic material over the conductivebarrier layer, and performing a planarization process, such as a CMPprocess or a mechanical grinding process, to remove excess portions ofthe conductive barrier layer and the metallic material from the topsurface of the IMD layer 108.

In FIG. 5, a plurality of memory cell layers are formed over theconductive vias 92 and the IMD layer 108. Specifically, a bit line layer114, a bottom electrode layer 116, a PCM layer 118, and a top electrodelayer 120 are deposited. The bit line layer 114 will be patterned insubsequent processing (see FIGS. 12A and 12B) to form bit lines 66 andbit line pads 68. The top electrode layer 120, the PCM layer 118, andthe bottom electrode layer 116 will also be patterned in subsequentprocessing (see FIGS. 18A and 18B) to form, respectively, the topelectrodes 86, the PCM elements 84, and the bottom electrodes 82 ofrespective PCRAM cells 58.

The bit line layer 114 is formed on the conductive vias 92 and the IMDlayer 108. The bit line layer 114 is formed of a metal such as tungsten,titanium, cobalt, nickel, the like, or combinations thereof, and may bedeposited by CVD, PVD, ALD, or the like. The bit line layer 114 isconformally formed, and may be formed using CVD, PVD, ALD,electro-chemical plating, electroless plating, or the like. In someembodiments, the bit line layer 114 is a layer of tungsten formed byCVD.

The bottom electrode layer 116 is formed on the bit line layer 114. Thebottom electrode layer 116 is formed of a conductive material such astitanium, tantalum, aluminum, tungsten, platinum, nickel, chromium,ruthenium, nitrides thereof, combinations thereof, multilayers thereof,or the like. The bottom electrode layer 116 is conformally formed, andmay be formed using CVD, PVD, ALD, electro-chemical plating, electrolessplating, or the like. In some embodiments, the bottom electrode layer116 is a layer of titanium nitride formed by PVD.

The PCM layer 118 is formed on the bottom electrode layer 116. The PCMlayer 118 is formed of a chalcogenide material. Chalcogenide materialsinclude at least a chalcogen anion (e.g., selenium (Se), tellurium (Te),and the like) and an electropositive element (e.g., germanium (Ge),silicon (Si), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi),zinc (Zn), nitrogen (N), boron (B), carbon (C), and the like). Anacceptable chalcogenide material includes, but is not limited to,GeSb₂Te₅ (GST). The PCM layer 118 is conformally formed, and may beformed using PVD, CVD, ALD, or the like. In some embodiments, the PCMlayer 118 is a layer of GST formed by PVD. Forming the PCM layer 118 byPVD allows for a good film quality and may reduce gap-filling concerns.

The top electrode layer 120 is formed on the PCM layer 118. The topelectrode layer 120 may be formed of a material that is selected fromthe same group of candidate materials of the bottom electrode layer 116,and may be formed using a method that is selected from the same group ofcandidate methods for forming the bottom electrode layer 116. The bottomelectrode layer 116 and the top electrode layer 120 may be formed fromthe same material, or may include different materials.

In FIGS. 6 through 12B, the bit line layer 114 is patterned to form bitlines 66 and bit line pads 68 (see FIGS. 12A and 12B). The top electrodelayer 120, the PCM layer 118, and the bottom electrode layer 116 arealso patterned to form top electrode strips 150, PCM strips 148, andbottom electrode strips 146 (see FIGS. 12A and 12B). This patterningprocess is the first of two patterning process performed to form thePCRAM cells 58 (see FIG. 2) in a self-aligned manner. In subsequentprocessing, the top electrode strips 150, the PCM strips 148, and thebottom electrode strips 146 will be patterned again to form the PCRAMcells 58.

As will be discussed in greater detail below, FIGS. 6 through 12Billustrate a process in which a first mask 136 (see FIG. 10) is formedhaving a pattern of the bit lines 66 and a second mask 138 (see FIGS.11A and 11B) is formed having a pattern of the bit line pads 68. In theillustrated embodiment, the first mask 136 is formed with amultiple-patterning process and the second mask 138 is formed with asingle-patterning process, so that the features of the first mask 136can be smaller than the features of the second mask 138. The bit linelayer 114 is then patterned using both masks 136, 138 as a combinedetching mask to simultaneously form the bit lines 66 and the bit linepads 68 (see FIGS. 12A and 12B).

In FIG. 6, a plurality of masking layers are formed over the memory celllayers, e.g., over the top electrode layer 120. Specifically, one ormore dielectric layers(s) 122 and a mandrel layer 124 are deposited. Thedielectric layers(s) 122 will be patterned to form etching masks, whichwill be used in subsequent processing to pattern the bit line layer 114.

The dielectric layers(s) 122 are formed on the top electrode layer 120.In the illustrated embodiment, the dielectric layers(s) 122 include afirst dielectric layer 122A over the top electrode layer 120 and asecond dielectric layer 122B over the first dielectric layer 122A. Thefirst dielectric layer 122A may be a mask layer, such as a hard masklayer; may be formed of a nitride such as silicon nitride, siliconoxynitride, titanium nitride, or the like; and may be formed bydeposition such as by PECVD, ALD, or the like. The second dielectriclayer 122B may be a pad layer; may be formed of an oxide such as siliconoxide, a TEOS oxide, or the like; and may be formed by deposition suchas by PECVD, ALD, or the like.

The mandrel layer 124 is formed on the dielectric layers(s) 122, e.g.,on the second dielectric layer 122B. The mandrel layer 124 is formed ofa material that has a high etching selectivity from the etching of theunderlying layer(s), e.g., the dielectric layers(s) 122. The mandrellayer 124 may be formed of a material such as amorphous silicon,polysilicon, silicon nitride, silicon oxide, the like, or combinationsthereof, and may be formed using a process such as a CVD, PECVD, or thelike.

One or more masks are formed over the mandrel layer 124. The masks willbe used to pattern the mandrel layer 124 and form mandrels. In someembodiments, the one or more masks may comprise one or more hard masks,a trilayer mask, a combination thereof, or the like. For example, a hardmask layer 126 can be formed over the mandrel layer 124 and aphotosensitive mask 128 can be formed over the hard mask layer 126. Insome embodiments, the hard mask layer 126 is formed of an oxide such assilicon oxynitride, silicon oxide, titanium oxide, a combinationthereof, or the like. The photosensitive mask 128 may be a photoresist,such as a single-layer photoresist, a bilayer photoresist, a trilayerphotoresist, or the like.

In FIG. 7, the mandrel layer 124 is patterned to form mandrels 130. Inthe illustrated embodiment, the pattern of the photosensitive mask 128is transferred to the hard mask layer 126, and the pattern of the hardmask layer 126 is then transferred to the mandrel layer 124. Eachpattern may be transferred by an acceptable etch process, such as areactive ion etch (RIE), neutral beam etch (NBE), the like, or acombination thereof. The etch may be anisotropic. In some embodiment,the final etch is selective to the mandrel layer 124, e.g., selectivelyetches the material of the mandrel layer 124 at a faster rate than thematerial of the underlying dielectric layer 122, e.g., the seconddielectric layer 122B. The photosensitive mask 128 and the hard masklayer 126 can optionally be removed with the material of the mandrellayer 124, or can be removed in a subsequent cleaning process.

After the patterning, the mandrels 130 can be separated by a spacingdistance D₃ in the range of about 40 nm to about 80 nm. Each of themandrels 130 can have a width W₁ in the range of about 40 nm to about 80nm. The mandrels 130 will be used to pattern spacers over the dielectriclayer(s) 122. The spacing distance D₃ and the width W₁ of the mandrels130 determines the spacing distance between the subsequently patternedspacers.

In FIG. 8, a spacer layer 132 is formed over the mandrels 130 and thedielectric layer(s) 122. After formation, the spacer layer 132 extendsalong the top surfaces of the mandrels 130, the sidewalls of themandrels 130, and the top surface of the underlying dielectric layer122, e.g., the second dielectric layer 122B. The spacer layer 132 isformed of a material that has a high etching selectivity from theetching of the underlying layer(s), e.g., the dielectric layer(s) 122.The spacer layer 132 may be formed from silicon nitride, aluminum oxide,aluminum nitride, tantalum nitride, titanium nitride, titanium oxide,the like, or combinations thereof, and may be formed using a processsuch as ALD, CVD, or the like. The spacer layer 132 has a high degree ofconformality, with the thickness T₁ of its vertical portions being equalto or slightly less than the thickness T₂ of its horizontal portions.For example, the thickness T₁ can be from about 80% to about 100% of thethickness T₂. The thickness T₁ can be in the range of about 15 nm toabout 30 nm and the thickness T₂ can be in the range of about 15 nm toabout 30 nm. The spacer layer 132 will be patterned to form spacers overthe dielectric layer(s) 122. The thickness T₁ of the vertical portionsof the spacer layer 132 determines the width of the subsequentlypatterned spacers.

In FIG. 9, the spacer layer 132 is patterned to form spacers 134 overthe dielectric layer(s) 122. A suitable etching process is performed toremove the horizontal portions of the spacer layer 132. The etchingprocess selectively etches the horizontal portions of the spacer layer132 at a faster rate than the mandrels 130 and the vertical portions ofthe spacer layer 132. For example, when the spacer layer 132 is formedof silicon nitride, the etching process can be an anisotropic dry etchperformed with methane (CH₄), chlorine (Cl₂), nitrogen (N₂), or thelike. After the etching process, the spacers 134 comprise the remainingvertical portions of the spacer layer 132. The mandrels 130 canoptionally be removed with the horizontal portions of the spacer layer132, or can be removed in a subsequent cleaning process. In someembodiments, the mandrels 130 are removed after the spacers 134 areformed, and can be removed by a suitable etching processes thatselectively etches the mandrels 130 at a faster rate than the spacers134.

After the patterning, the spacers 134 have a width W₂ and are separatedby a spacing distance D₄. The spacing distance D₄ between the spacers134 can be in the range of about 20 nm to about 50 nm, and the width W₂of the spacers 134 can be in the range of about 15 nm to about 30 nm. Asnoted above, the spacing distance D₃ and the width W₁ (see FIG. 7) ofthe mandrels 130 determines the spacing distance D₄ between the spacers134, and the thickness T₁ (see FIG. 8) of the vertical portions of thespacer layer 132 determines the width W₂ of the spacers 134. Becauseselective etching process are used to form the spacers 134, thethickness T₁ of the vertical portions of the spacer layer 132 decreasesby a small amount when forming the spacers 134. The spacers 134 will beused to pattern the bit line layer 114. The spacing distance D₄ and thewidth W₂ of the spacers 134 determines the spacing distance and thewidth of the resulting bit lines 66 (see FIGS. 12A and 12B).

In FIG. 10, the spacers 134 in undesired locations are removed in a cutprocess. The cut process may be performed using suitablephotolithography and etching techniques. For example, a first subset ofthe spacers 134 may be covered with, e.g., a mask such as a photoresist,and an uncovered second subset of the spacers 134 may then be removedwith an etch that selectively etches the material of the spacers 134 ata faster rate than the material of the underlying dielectric layer 122,e.g., the second dielectric layer 122B. In some embodiments, the spacers134 are initially formed in both the logic region 50L and memory region50M, and the cut process is used to remove the spacers 134 from thelogic region 50L, the first pad region 50P₁, and the second pad region50P₂ so that the spacers 134 only remain in the cell region 50C. Theremaining spacers 134 form a first mask 136 in the cell region 50C.

In FIG. 11A, a second mask 138 is formed in the first pad region 50P₁.The second mask 138 may be photosensitive mask, such as a photoresist,such as a single-layer photoresist, a bilayer photoresist, a trilayerphotoresist, or the like. The second mask 138 is not formed bypatterning spacers, and as such, the features of the second mask 138 arelarger than the features of the first mask 136. For example, thefeatures of the second mask 138 can have a width W₃ that is larger thanthe width W₂ (see FIG. 9). For example, the width W₃ can be in the rangeof about 50 nm to about 500 nm.

As shown by FIG. 11B, portions of the first mask 136 and portions of thesecond mask 138 overlap. Thus, some of the patterned features will becontinuous with one another. Further, as will be discussed in greaterdetail below, the bit lines 66 extend along the same direction D₁ (seeFIG. 12B). The spacers 134, which will be used to pattern the bit lines66, thus also extend along the same direction D₁.

In FIG. 12A, the masks 136, 138 are used as a combined etching mask toetch and pattern the dielectric layer(s) 122. At least one of thedielectric layer(s) 122, e.g., the first dielectric layer 122A, remainsafter the etching and forms a patterned hard mask. The patterned hardmask is then used as an etching mask to etch and pattern the topelectrode layer 120, the PCM layer 118, the bottom electrode layer 116,and the bit line layer 114. The patterning may include one or moreetching processes. The etching method may include a plasma etchingmethod, such as ion beam etching (IBE). IBE offers a high level ofprecision (e.g., high anisotropism), which can help control the profileof the resulting bit lines 66. The etching may be implemented using glowdischarge plasma (GDP), capacitive coupled plasma (CCP), inductivelycoupled plasma (ICP), or the like. The first mask 136, the second mask138, and/or the dielectric layer(s) 122 may be consumed in the etchingprocess, or may be removed after the etching process. In the illustratedembodiment, the first dielectric layer 122A remains after the etchingprocess.

The etching process forms bit lines 66 and bit line pads 68. The bitlines 66 and the bit line pads 68 are disposed beneath the top electrodestrips 150. The bit lines 66 and the bit line pads 68 comprise remainingportions of the bit line layer 114.

The etching process also forms top electrode strips 150, PCM strips 148,and bottom electrode strips 146. The top electrode strips 150, the PCMstrips 148, and the bottom electrode strips 146 comprise remainingportions of the top electrode layer 120, the PCM layer 118, and thebottom electrode layer 116, respectively. Although not shown, it shouldbe appreciated that the patterned layers can have sloped sidewalls, andcan have trapezoidal shapes in the illustrated cross-section. Each ofthe patterned layers has the same shape in the top-down view as thecombined shape of the masks 136, 138 (see FIG. 11B).

As shown by FIG. 12B, each of the bit lines 66 are metal strips thatextend along the same direction D₁ and emanate from a bit line pad 68.Thus, although the bit lines 66 and the bit line pads 68 are illustratedas separate elements, it should be appreciated that each bit line pad 68and its corresponding bit lines 66 are actually a single continuousconductive feature that is patterned from the bit line layer 114. Inother words, the patterning shown in FIG. 12A forms first conductivefeatures that have bit line portions and bit line pad portions.

It should be appreciated that FIGS. 6 through 12B illustrate an exampleprocess for patterning the bit line layer 114, and other processes maybe used to pattern the bit line layer 114. For example, the bit linelayer 114 may also be patterned using next-generation lithographytechniques such as extreme ultraviolet (EUV) lithography, deepultraviolet (DUV) lithography, X-ray lithography, soft X-ray (SX)lithography, ion beam projection lithography, electron-beam projectionlithography, or the like. The use of next-generation lithographytechniques may allow the bit line layer 114 to be patterned by asingle-patterning photolithography process, obviating the need formultiple-patterning photolithography processes.

In FIG. 13, spacers 156 are formed on the sidewalls of the bit line pads68 and the bit lines 66. The spacers 156 are also formed on thesidewalls of the top electrode strips 150, the PCM strips 148, and thebottom electrode strips 146. The spacers 156 may be formed byconformally depositing an insulating material and then etching theinsulating material. The insulating material may be a nitride (e.g.,silicon nitride, aluminum nitride, etc.), an oxide (e.g., silicon oxide,aluminum oxide, etc.), a carbide (e.g., silicon carbide), combinationsthereof (e.g., silicon oxynitride, silicon carbonitride, etc.),multilayers thereof, or the like. The etch may be anisotropic.

An IMD layer 158 is then formed over the spacers 156, the IMD layer 108,and the first dielectric layer 122A (if present) or the top electrodestrips 150. The IMD layer 158 may be formed of a material that isselected from the same group of candidate materials of the IMD layer108, and may be formed using a method that is selected from the samegroup of candidate methods for forming the IMD layer 108. The IMD layer108 and the IMD layer 158 may be formed from the same material, or mayinclude different materials.

In FIG. 14, a planarization process is performed to remove excessmaterial of the IMD layer 158. The planarization process can be a CMP,mechanical grinding, an etchback, or the like. The planarization processremoves the first dielectric layer 122A (if present) to expose the topelectrode strips 150. After the planarization process, top surfaces ofthe IMD layer 158, the spacers 156, and the top electrode strips 150 arecoplanar (within process variations).

In FIG. 15, a word line layer 160 is formed on the planarized topsurfaces of the IMD layer 158, the spacers 156, and the top electrodestrips 150. The word line layer 160 may be formed of a material that isselected from the same group of candidate materials of the bit linelayer 114, and may be formed using a method that is selected from thesame group of candidate methods for forming the bit line layer 114. Thebit line layer 114 and the word line layer 160 may be formed from thesame material, or may include different materials.

In FIGS. 16 through 18B, the word line layer 160 is patterned to formword lines 62 and word line pads 64 (see FIGS. 18A and 18B). The topelectrode strips 150, the PCM strips 148, and the bottom electrodestrips 146 are also patterned during the process for patterning the wordline layer 160, thus forming PCRAM cell 58 (see FIGS. 18A and 18B). Thispatterning process is the second of the two patterning process performedto form the PCRAM cells 58 (see FIGS. 18A and 18B) in a self-alignedmanner.

As will be discussed in greater detail below, FIGS. 16 through 18Billustrate a process in which a third mask 166 (see FIG. 16) is formedhaving a pattern of the word lines 62 and a fourth mask 168 (see FIGS.17A and 17B) is formed having a pattern of the word line pads 64. In theillustrated embodiment, the third mask 166 is formed with amultiple-patterning process and the fourth mask 168 is formed with asingle-patterning process, so that the features of the third mask 166can be smaller than the features of the fourth mask 168. The word linelayer 160 is then patterned using both masks 166, 168 as a combinedetching mask to simultaneously form the word lines 62 and the word linepads 64 (see FIGS. 18A and 18B).

In FIG. 16, a plurality of masking layers are formed over the word linelayer 160. Specifically, one or more dielectric layers(s) 162 aredeposited. The dielectric layers(s) 162 will be patterned to formetching masks, which will be used in subsequent processing to patternthe word line layer 160.

The dielectric layers(s) 162 are formed on the word line layer 160. Inthe illustrated embodiment, the dielectric layers(s) 162 include a firstdielectric layer 162A over the word line layer 160 and a seconddielectric layer 162B over the first dielectric layer 162A. The firstdielectric layer 162A may be a mask layer, such as a hard mask layer;may be formed of a nitride such as silicon nitride, silicon oxynitride,titanium nitride, or the like; and may be formed by deposition such asby PECVD, ALD, or the like. The second dielectric layer 162B may be apad layer; may be formed of an oxide such as silicon oxide, a TEOSoxide, or the like; and may be formed by deposition such as by PECVD,ALD, or the like.

Spacers 164 are then formed over the dielectric layer(s) 162. Thespacers 164 may be formed of a material that is selected from the samegroup of candidate materials of the spacers 134, and may be formed usinga method that is selected from the same group of candidate methods forforming the spacers 134. For example, the spacers 164 can be formed bydepositing a mandrel layer (see, e.g., FIG. 6), patterning the mandrellayer to form mandrels (see, e.g., FIG. 7), depositing a spacer layerover the mandrels (see, e.g., FIG. 8), patterning the spacer layer toform the spacers 164 (see, e.g., FIG. 9), and removing spacers 164 inundesired locations in a cut process (see, e.g., FIG. 10). The spacers134 and the spacers 164 may be formed from the same material, or mayinclude different materials. The remaining spacers 164 form a third mask166 in the cell region 50C, which will be used to pattern the word linelayer 160.

In FIG. 17A, a fourth mask 168 is formed in the second pad region 50P₂.The fourth mask 168 may be photosensitive mask, such as a photoresist,such as a single-layer photoresist, a bilayer photoresist, a trilayerphotoresist, or the like. The fourth mask 168 is not formed bypatterning spacers, and as such, the features of the fourth mask 168 arelarger than the features of the third mask 166. In some embodiments, thefeatures of the third mask 166 and the fourth mask 168 have similardimensions as the features of the first mask 136 and the second mask138, respectively. In some embodiments, the features of the third mask166 and the fourth mask 168 have different dimensions than the featuresof the first mask 136 and the second mask 138.

As shown by FIG. 17B, portions of the third mask 166 and portions of thefourth mask 168 overlap. Thus, some of the patterned features will becontinuous with one another. Further, as will be discussed in greaterdetail below, the word lines 62 extend along the same direction D₂ (seeFIG. 18B). The spacers 164, which will be used to pattern the word lines62, thus also extend along the same direction D₂.

In FIG. 18A, the masks 166, 168 are used as a combined etching mask toetch and pattern the dielectric layer(s) 162. At least one of thedielectric layer(s) 162, e.g., the first dielectric layer 162A, remainsafter the etching and forms a patterned hard mask. The patterned hardmask is then used as an etching mask to etch and pattern the word linelayer 160, the top electrode strips 150, the PCM strips 148, and thebottom electrode strips 146. The patterning may include one or moreetching processes, and can form recesses 170 in the IMD layer 158. Theetching method may include a plasma etching method, such as ion beametching (IBE). IBE offers a high level of precision (e.g., highanisotropism), which can help control the profile of the resulting wordlines 62. The etching may be implemented using glow discharge plasma(GDP), capacitive coupled plasma (CCP), inductively coupled plasma(ICP), or the like. The third mask 166, the fourth mask 168, and/or thedielectric layer(s) 162 may be consumed in the etching process, or maybe removed after the etching process. In the illustrated embodiment, thefirst dielectric layer 162A remains after the etching process.

The etching process forms word lines 62 and word line pads 64. The wordlines 62 are disposed over top electrodes 86 and the word line pads 64are disposed over unpatterned portions of the IMD layer 158. The wordlines 62 and the word line pads 64 comprise remaining portions of theword line layer 160. Although not shown, it should be appreciated thatthe word lines 62 can have sloped sidewalls, and can have trapezoidalshapes in the illustrated cross-section. The patterned word line layer160 has the same shape in the top-down view as the combined shape of themasks 166, 168 (see FIG. 17B).

As shown by FIG. 18B, each of the word lines 62 are metal strips thatextend along the same direction D₂ and emanate from a word line pad 64.Thus, although the word lines 62 and the word line pads 64 areillustrated as separate elements, it should be appreciated that eachword line pad 64 and its corresponding word lines 62 are actually asingle continuous conductive feature that is patterned from the wordline layer 160. In other words, the patterning shown in FIG. 18A formssecond conductive features that have word line portions and word linepad portions.

The etching process also patterns the top electrode strips 150, the PCMstrips 148, and the bottom electrode strips 146 to form the bottomelectrodes 82, the PCM elements 84, and the top electrodes 86,respectively, which together form the PCRAM cells 58. Each PCRAM cell 58includes a bottom electrode 82, a PCM element 84, and a top electrode86, with the PCM element 84 being disposed between the bottom electrode82 and the top electrode 86. The bottom electrodes 82 comprise remainingportions of the bottom electrode strips 146. The PCM elements 84comprise remaining portions of the PCM strips 148. The top electrodes 86comprise remaining portions of the top electrode strips 150. Althoughnot shown, it should be appreciated that the bottom electrodes 82, thePCM elements 84, and the top electrodes 86 can have sloped sidewalls,and can have trapezoidal shapes in the illustrated cross-section.

The etching process removes the portions of the top electrode strips150, the PCM strips 148, and the bottom electrode strips 146 that areuncovered by the masks 166, 168, such as the portions of those layersover the bit line pads 68. Thus, as shown by FIG. 18B, each PCRAM cell58 is disposed at an intersection of a word line 62 and a bit line 66 inthe top-down view. The PCRAM cells 58 are thus formed in a self-alignedmanner, which allows the spacing distance D₅ and the width W₄ of thePCRAM cells 58 to be small. For example, the spacing distance D₅ can bein the range of about 20 nm to about 50 nm, and the width W₄ can be inthe range of about 15 nm to about 30 nm. The spacing distance D₅corresponds to both the distance between adjacent PCRAM cells 58, andalso the distance between adjacent intersections of the word lines 62and the bit lines 66.

The recesses 170 are formed in portions of the IMD layer 158.Specifically, the recesses 170 are formed by etching the IMD layer 158and any top electrode strips 150, PCM strips 148, or bottom electrodestrips 146 that are uncovered by the masks 166, 168. Thus, the recesses170 expose the bit line pads 68. Timed etch processes may be used tostop the etching of the recesses 170 after the recesses 170 reach adesired depth. Although not shown in FIG. 18A, it should be appreciatedthat the recesses 170 also expose portions of the bit lines 66 that arenot disposed beneath the word lines 62 and the word line pads 64. Therecesses 170 can be formed by performing the etching process (describedabove) with multiple etches. For example, the etching process caninclude a first etch and a second etch. The first etch can selectivelyetch the material of the word line layer 160 at a faster rate than thematerials of the IMD layer 158, the top electrode strips 150, the PCMstrips 148, and the bottom electrode strips 146. The second etch canselectively etch the materials of the IMD layer 158, the top electrodestrips 150, the PCM strips 148, and the bottom electrode strips 146 at afaster rate than the material of the bit lines 66 and the bit line pad68. In some embodiments, the first etch is ion beam etching using sulfurhexafluoride (SF₆), argon (Ar), oxygen (O₂), and difluoromethane (CH₂F₂)for a duration in a range of 20 seconds to 60 seconds, and the secondetch is ion beam etching using chlorine (Cl₂), hydrogen bromide (HBr),argon (Ar), and difluoromethane (CH₂F₂) for a duration in a range of 15seconds to 75 seconds. Other etching parameters may be used whenmanufacturing magnetoresistive random-access memories (MRAMs), resistiverandom access memories (RRAMs), memories with a selector structure, orthe like. Further, the etching parameters can be varied based on thematerials of the etched films and the film thicknesses.

After the recesses 170 are formed, the IMD layer 158 includes recessedportions 158R and unrecessed portions 158U. The recessed portions 158Rsurround bit lines 66 and the bit line pads 68, and the unrecessedportions 158U surround the PCRAM cells 58. The recessed portions 158Rare disposed beneath the word lines 62 and the word line pads 64. Therecessed portions 158R are unpatterned and thus have a greater heightthan the unrecessed portions 158U.

It should be appreciated that FIGS. 16 through 18B illustrate an exampleprocess for patterning the word line layer 160, and other processes maybe used to pattern the word line layer 160. For example, the word linelayer 160 may also be patterned using next-generation lithographytechniques such as extreme ultraviolet (EUV) lithography, deepultraviolet (DUV) lithography, X-ray lithography, soft X-ray (SX)lithography, ion beam projection lithography, electron-beam projectionlithography, or the like. The use of next-generation lithographytechniques may allow the word line layer 160 to be patterned by asingle-patterning photolithography process, obviating the need formultiple-patterning photolithography processes.

In FIG. 19, an IMD layer 178 is formed over the IMD layer 158, the bitline pads 68, and the first dielectric layer 162A (if present) or theword lines 62 and the word line pads 64. The IMD layer 178 may be formedof a material that is selected from the same group of candidatematerials of the IMD layer 108, and may be formed using a method that isselected from the same group of candidate methods for forming the IMDlayer 108. The IMD layer 108 and the IMD layer 178 may be formed fromthe same material, or may include different materials. After formation,the IMD layer 178 is disposed over the bit lines 66 and the recessedportions 158R of the IMD layer 158. The IMD layer 178 thus surrounds theword lines 62, the word line pads 64, and the unrecessed portions 158Uof the IMD layer 158. Further, the combination of the IMD layers 158,178 surround the PCRAM cells 58 on all four sides. Confining all foursides of the PCRAM cells 58 in a dielectric material can improve theperformance of the PCRAM cells 58 during operation, as the dielectricmaterial helps absorb heat that is generated when the PCM elements 84change phases.

In FIG. 20, a planarization process is performed to remove excessmaterial of the IMD layer 178. The planarization process can be a CMP,mechanical grinding, an etchback, or the like. The planarization processremoves the first dielectric layer 162A (if present) to expose the wordlines 62 and the word line pads 64. After the planarization process, topsurfaces of the IMD layer 178, the word line pads 64, and the word lines62 are coplanar (within process variations).

In FIG. 21A, an etch stop layer 182 is formed on the planarized topsurfaces of the IMD layer 178, the word line pads 64, and the word lines62. The etch stop layer 182 may be formed of a material that is selectedfrom the same group of candidate materials of the etch stop layer 106,and may be formed using a method that is selected from the same group ofcandidate methods for forming the etch stop layer 106. The etch stoplayer 106 and the etch stop layer 182 may be formed from the samematerial, or may include different materials.

An IMD layer 184 is then formed on the etch stop layer 182. The IMDlayer 184 may be formed of a material that is selected from the samegroup of candidate materials of the IMD layer 108, and may be formedusing a method that is selected from the same group of candidate methodsfor forming the IMD layer 108. The IMD layer 108 and the IMD layer 184may be formed from the same material, or may include differentmaterials.

Conductive features 186 (e.g., interconnects) are then formed extendingthrough the IMD layer 184 and the etch stop layer 182. The conductivefeatures 186 include conductive vias 186V (which can correspond to themetal vias V5, see FIG. 2, and to the conductive vias 94, see FIG. 1)and conductive lines 186L (which can correspond to the metal lines L5,see FIG. 2). The conductive features 186 are formed in both the memoryregion 50M and the logic region 50L. The conductive features 186 may beformed by a damascene process, such as a single damascene process, adual damascene process, or the like. The conductive features 186 areelectrically coupled to the memory devices (e.g., PCRAMs) formed in thememory region 50M and the logic devices (e.g., logic circuits) formed inthe logic region 50L. A first subset of the conductive features 186A areformed in the memory region 50M, and are connected to the word line pads64. A second subset of the conductive features 186B are formed in thelogic region 50L, and further extend though the IMD layer 178, the IMDlayer 158, the IMD layer 108, and the etch stop layer 106 to beconnected to the conductive features 104. In some embodiments, theconductive features 186 electrically couple the memory devices to thelogic devices. For example, the conductive features 186 can be used toelectrically couple some of the conductive features 104 to some of theword line pads 64, such as in the illustrated metallization layer, or inanother metallization layer. Although each conductive via 186V andcorresponding conductive line 186L is illustrated as a separate element,it should be appreciated that they may be a continuous conductivefeature, such as in embodiments where they are formed by a dualdamascene process.

Each PCRAM cell 58 is connected to a conductive feature 186 and aconductive feature 104. Specifically, each top electrode 86 is connectedto a conductive line 186L by a word line 62, a word line pad 64, and aconductive via 94. Likewise, each bottom electrode 82 is connected to aconductive feature 104 by a bit line 66, a bit line pad 68, and aconductive via 92. The word line pads 64 are disposed under and arephysically and electrically coupled to the conductive vias 94. The bitline pads 68 are disposed over and are physically and electricallycoupled to the conductive vias 92. Thus, the conductive vias 92 connectthe bit line pads 68 to conductive features (e.g., interconnects) of anunderlying metallization pattern (e.g., metallization layer M4 in FIG.2), and the conductive vias 94 connect the word line pads 64 toconductive features (e.g., interconnects) of an overlying metallizationpattern (e.g., metallization layer M6 in FIG. 2). Further, theconductive features 186B connect the conductive features of theunderlying metallization pattern to the conductive features of theoverlying metallization pattern.

As shown by FIG. 21B, The bit lines 66 emanating from each bit line pad68 can be interleaved. For example, the bit lines 66 emanating from afirst bit line pad 68A can be interleaved with the bit lines 66emanating from a second bit line pad 68B. Similarly, the word lines 62emanating from each word line pad 64 can be interleaved. For example,the word lines 62 emanating from a first word line pad 64A can beinterleaved with the word lines 62 emanating from a second word line pad64B.

FIG. 22 is a cross-sectional view of the semiconductor device 50, inaccordance with some other embodiments. This embodiment is similar tothe embodiment described with respect to FIG. 21A, except ovonicthreshold switching (OTS) layers 192 are formed between the bottomelectrodes 82 and the bit lines 66. The OTS layers 192 may be formed ofa chalcogenide material, and can be formed of a different chalcogenidematerial than the PCM elements 84. The OTS layers 192 may be used formemory selectors. Memory selectors function similar to transistors,having a threshold voltage (V_(th)) value. Only applied voltages largerthan the V_(th) of a PCRAM cell 58 can create a current path to thePCRAM cell 58, thus enabling memory read/write operations.

FIGS. 23A through 23E are three-dimensional views of intermediate stagesin a self-aligned patterning process for forming the PCRAM cells, inaccordance with some embodiments. FIGS. 23A through 23E are simplifiedviews, and some features are omitted for clarity of illustration. FIGS.23A through 23E illustrate additional views of the semiconductor device50 during the process described above with respect to FIGS. 3 through21B.

In FIG. 23A, the bit line layer 114 is deposited over a substrate, andthe memory cell layers (e.g., the bottom electrode layer 116, the PCMlayer 118, and the top electrode layer 120) are deposited over the bitline layer 114. The bit line layer 114 and the memory cell layers aredeposited in the manner described with respect to FIG. 5.

In FIG. 23B, the bottom electrode layer 116, the PCM layer 118, the topelectrode layer 120, and the bit line layer 114 are patterned.Patterning the bit line layer 114 forms the bit lines 66 and the bitline pads 68. Patterning the bottom electrode layer 116, the PCM layer118, and the top electrode layer 120 forms the bottom electrode strips146, the PCM strips 148, and the top electrode strips 150, respectively.The bottom electrode strips 146, the PCM strips 148, the top electrodestrips 150, and the bit lines 66 each extend in the first direction D₁.The bottom electrode layer 116, the PCM layer 118, the top electrodelayer 120, and the bit line layer 114 are patterned in the mannerdescribed with respect to FIGS. 6 through 12B.

In FIG. 23C, the IMD layer 158 is deposited around the bottom electrodestrips 146, the PCM strips 148, the top electrode strips 150, the bitlines 66, and the bit line pads 68. The IMD layer 158 is then planarizedto expose the top electrode strips 150. The IMD layer 158 is depositedand planarized in the manner described with respect to FIGS. 13 and 14.

In FIG. 23D, the word line layer 160 is deposited over the IMD layer158, the top electrode strips 150, and the other underlying strips. Theword line layer 160 is deposited in the manner described with respect toFIG. 15.

In FIG. 23E, the word line layer 160, the bottom electrode strips 146,the PCM strips 148, and the top electrode strips 150 are patterned.Patterning the word line layer 160 forms the word lines 62 and the wordline pads 64. Patterning the bottom electrode strips 146, the PCM strips148, and the top electrode strips 150 forms the PCRAM cells 58. The wordlines 62 each extend in the second direction D₂, which is perpendicularto the first direction D₁. As noted above, the PCRAM cells 58 are eachdisposed at an intersection of a word line 62 and a bit line 66 in atop-down view. The word line layer 160, the bottom electrode strips 146,the PCM strips 148, and the top electrode strips 150 are patterned inthe manner described with respect to FIGS. 16 through 18B.

Embodiments may achieve advantages. Forming the PCRAM cells 58 in aself-aligned manner with multiple patterning processes allows the PCRAMcells 58 to be formed with smaller spacing distances and widths, therebyimproving the density and the performance of the PCRAM cells 58.Specifically, smaller PCRAM cells 58 generate less heat when their PCMelements 84 change phases. Further, embodiments patterning processesallow the word lines 62 and the bit lines 66 for the PCRAM array to besimultaneously patterned with the PCRAM cells 58, allowing manufacturingcosts to be reduced.

In an embodiment, a device includes: a first metallization layer over asubstrate, the substrate including active devices; a first bit line overthe first metallization layer, the first bit line connected to firstinterconnects of the first metallization layer, the first bit lineextending in a first direction, the first direction parallel to gates ofthe active devices; a first phase-change random access memory (PCRAM)cell over the first bit line; a word line over the first PCRAM cell, theword line extending in a second direction, the second directionperpendicular to the gates of the active devices; and a secondmetallization layer over the word line, the word line connected tosecond interconnects of the second metallization layer.

In some embodiments, the device further includes: a second bit line overthe first metallization layer, the second bit line extending in thefirst direction; and a second PCRAM cell over the second bit line, theword line disposed over the second PCRAM cell, the first PCRAM cellbeing separated from the second PCRAM cell by a distance in a range of20 nm to 50 nm. In some embodiments of the device, the first PCRAM celland the second PCRAM cell each have a width in a range of 15 nm to 30nm. In some embodiments, the device further includes: a bit line padover the first metallization layer, the bit line pad and the first bitline being a first continuous conductive feature; a first conductive viaconnecting the bit line pad to the first interconnects of the firstmetallization layer; and a first inter-metal dielectric (IMD) layeraround the first conductive via, the first continuous conductive featuredisposed on the first IMD layer. In some embodiments, the device furtherincludes: a word line pad over the bit line pad, the word line pad andthe word line being a second continuous conductive feature; a secondconductive via connecting the word line pad to the second interconnectsof the second metallization layer; and a second IMD layer around thesecond conductive via, the second IMD layer disposed on the secondcontinuous conductive feature. In some embodiments, the device furtherincludes: a third conductive via extending through the first IMD layerand the second IMD layer, the third conductive via connecting the firstinterconnects of the first metallization layer to the secondinterconnects of the second metallization layer. In some embodiments,the device further includes: a first dielectric layer having a firstportion and a second portion, the first portion surrounding the firstbit line, the second portion surrounding the first PCRAM cell, the firstportion having a first height, the second portion having a secondheight, the second height being greater than the first height, the wordline disposed over the second portion. In some embodiments, the devicefurther includes: a second dielectric layer over the first bit line andthe first portion of the first dielectric layer, the second dielectriclayer surrounding the word line and the second portion of the firstdielectric layer. In some embodiments of the device, the first PCRAMcell includes: a bottom electrode connected to the first bit line; a topelectrode connected to the word line; and a phase change material (PCM)element between the top electrode and the bottom electrode. In someembodiments, the device further includes: an ovonic threshold switchinglayer between the bottom electrode and the first bit line.

In an embodiment, a device includes: a first inter-metal dielectric(IMD) layer; a first conductive via extending through the first IMDlayer; a first conductive feature having a bit line pad portion and abit line portion, the bit line pad portion disposed on the firstconductive via, the bit line portion disposed on the first IMD layer; aphase-change random access memory (PCRAM) cell on the bit line portionof the first conductive feature; a second IMD layer surrounding thePCRAM cell and the first conductive feature; and a second conductivefeature having a word line pad portion and a word line portion, the wordline pad portion disposed on the second IMD layer, the word line portiondisposed on the PCRAM cell.

In some embodiments, the device further includes: a second conductivevia on the word line pad portion of the second conductive feature; and athird IMD layer surrounding the second conductive via.

In an embodiment, a method includes: forming a bit line layer over asubstrate including active devices; depositing a phase change material(PCM) layer over the bit line layer; patterning the PCM layer and thebit line layer to form a PCM strip and a bit line, respectively, the PCMstrip and the bit line each extending in a first direction in a top-downview, the first direction parallel to gates of the active devices;depositing a first inter-metal dielectric (IMD) layer around the PCMstrip and the bit line; depositing a word line layer over the first IMDlayer and the PCM strip; and patterning the word line layer and the PCMstrip to form a word line and a PCM element, respectively, the word lineextending in a second direction in the top-down view, the seconddirection perpendicular to the gates of the active devices, the PCMelement disposed at an intersection of the word line and the bit line inthe top-down view.

In some embodiments of the method, patterning the PCM layer and the bitline layer includes: forming a first mask over the PCM layer, featuresof the first mask extending in the first direction, the features of thefirst mask having a first width; forming a second mask over the PCMlayer, features of the second mask extending in the second direction,the features of the second mask having a second width, portions of thefirst mask and the second mask overlapping; and etching the PCM layerand the bit line layer using the first mask and the second mask as afirst combined etching mask to form a first conductive feature, thefirst conductive feature including the bit line and a bit line pad. Insome embodiments of the method, patterning the word line layer and thePCM strip includes: forming a third mask over the word line layer,features of the third mask having the first width; forming a fourth maskover the PCM layer, features of the fourth mask having the second width,portions of the third mask and the fourth mask overlapping; and etchingthe word line layer and the PCM strip using the third mask and thefourth mask as a second combined etching mask to form a secondconductive feature, the second conductive feature including the wordline and a word line pad. In some embodiments of the method, etching theword line layer and the PCM strip includes: etching the word line layerwith ion beam etching using hexafluoride (SF₆), argon (Ar), oxygen (O₂),and difluoromethane (CH₂F₂) for a duration in a range of 20 seconds to60 seconds; and etching the PCM strip and the first IMD layer with ionbeam etching using chlorine (Cl₂), hydrogen bromide (HBr), argon (Ar),and difluoromethane (CH₂F₂) for a duration in a range of 15 seconds to75 seconds. In some embodiments, the method further includes: depositingthe bit line layer on a first conductive via, the bit line padcontacting the first conductive via; and forming a second conductive viacontacting the word line pad. In some embodiments of the method,patterning the word line layer and the PCM strip includes exposing aportion of the bit line layer covered by the PCM strip. In someembodiments of the method, patterning the word line layer and the PCMstrip includes recessing a portion of the first IMD layer, the word linedisposed on an unrecessed portion of the first IMD layer. In someembodiments, the method further includes: depositing a second IMD layeraround the word line and the unrecessed portion of the first IMD layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a bit line layerover a substrate comprising active devices; depositing a phase changematerial (PCM) layer over the bit line layer; patterning the PCM layerand the bit line layer to form a PCM strip and a bit line, respectively,the PCM strip and the bit line each extending in a first direction in atop-down view, the first direction parallel to gates of the activedevices; depositing a first inter-metal dielectric (IMD) layer aroundthe PCM strip and the bit line; depositing a word line layer over thefirst IMD layer and the PCM strip; and patterning the word line layerand the PCM strip to form a word line and a PCM element, respectively,the word line extending in a second direction in the top-down view, thesecond direction perpendicular to the gates of the active devices, thePCM element disposed at an intersection of the word line and the bitline in the top-down view.
 2. The method of claim 1, wherein patterningthe PCM layer and the bit line layer comprises: forming a first maskover the PCM layer, features of the first mask extending in the firstdirection, the features of the first mask having a first width; forminga second mask over the PCM layer, features of the second mask extendingin the second direction, the features of the second mask having a secondwidth, portions of the first mask and the second mask overlapping; andetching the PCM layer and the bit line layer using the first mask andthe second mask as a first combined etching mask to form a firstconductive feature, the first conductive feature comprising the bit lineand a bit line pad.
 3. The method of claim 2, wherein patterning theword line layer and the PCM strip comprises: forming a third mask overthe word line layer, features of the third mask having the first width;forming a fourth mask over the PCM layer, features of the fourth maskhaving the second width, portions of the third mask and the fourth maskoverlapping; and etching the word line layer and the PCM strip using thethird mask and the fourth mask as a second combined etching mask to forma second conductive feature, the second conductive feature comprisingthe word line and a word line pad.
 4. The method of claim 3, whereinetching the word line layer and the PCM strip comprises: etching theword line layer with ion beam etching using hexafluoride (SF₆), argon(Ar), oxygen (O₂), and difluoromethane (CH₂F₂) for a duration in a rangeof 20 seconds to 60 seconds; and etching the PCM strip and the first IMDlayer with ion beam etching using chlorine (Cl₂), hydrogen bromide(HBr), argon (Ar), and difluoromethane (CH₂F₂) for a duration in a rangeof 15 seconds to 75 seconds.
 5. The method of claim 3 furthercomprising: depositing the bit line layer on a first conductive via, thebit line pad contacting the first conductive via; and forming a secondconductive via contacting the word line pad.
 6. The method of claim 1,wherein patterning the word line layer and the PCM strip comprisesexposing a portion of the bit line layer covered by the PCM strip. 7.The method of claim 1, wherein patterning the word line layer and thePCM strip comprises recessing a portion of the first IMD layer, the wordline disposed on an unrecessed portion of the first IMD layer.
 8. Themethod of claim 7 further comprising: depositing a second IMD layeraround the word line and the unrecessed portion of the first IMD layer.9. A method comprising: depositing a phase change material (PCM) layerover a bit line layer; patterning the PCM layer and the bit line layerwith a first patterning process to form a PCM strip and a bit line,respectively, the PCM strip and the bit line each extending in a firstdirection in a top-down view; depositing a first inter-metal dielectricaround the PCM strip and the bit line; depositing a word line layer overthe first inter-metal dielectric and the PCM strip; and patterning theword line layer and the PCM strip with a second patterning process toform a word line and a PCM element, respectively, the word lineextending in a second direction in the top-down view, the seconddirection perpendicular to the first direction, the PCM element disposedat an intersection of the word line and the bit line in the top-downview.
 10. The method of claim 9, wherein the first patterning process isa multiple-patterning process.
 11. The method of claim 9, wherein thesecond patterning process is a multiple-patterning process.
 12. Themethod of claim 9, wherein the first patterning process comprises afirst ion beam etching process, and the second patterning processcomprises a second ion beam etching process.
 13. The method of claim 9further comprising: depositing a second inter-metal dielectric aroundthe word line and the PCM element.
 14. The method of claim 13, whereinpatterning the PCM strip exposes a portion of the bit line layer, andthe second inter-metal dielectric is deposited on the portion of the bitline layer.
 15. The method of claim 9 further comprising: recessing afirst portion of the first inter-metal dielectric with the secondpatterning process, the word line disposed on a second portion of thefirst inter-metal dielectric, the second portion of the firstinter-metal dielectric not recessed by the second patterning process.16. A method comprising: depositing a memory cell layer on a firstconductive layer; patterning the memory cell layer and the firstconductive layer to form a memory cell strip and a first conductivefeature, respectively, the first conductive feature comprising a bitline pad portion and a bit line portion, the bit line portion extendingin a first direction; depositing a second conductive layer on the memorycell strip; and patterning the second conductive layer and the memorycell strip to form a second conductive feature and a memory element,respectively, the second conductive feature comprising a word line padportion and a word line portion, the word line portion extending in asecond direction, the second direction perpendicular to the firstdirection, the memory element disposed at an intersection of the wordline portion and the bit line portion.
 17. The method of claim 16further comprising: forming a first conductive via on the word line padportion, wherein the bit line pad portion is formed on a secondconductive via.
 18. The method of claim 16, wherein the memory celllayer is a phase change material layer.
 19. The method of claim 16,wherein patterning the memory cell layer and the first conductive layercomprises: forming a first mask over the memory cell layer, the firstmask having a pattern of the bit line portion; forming a second maskover the memory cell layer, the second mask having a pattern of the bitline pad portion; and etching the memory cell layer and the firstconductive layer using the first mask and the second mask as a firstcombined etching mask.
 20. The method of claim 19, wherein patterningthe second conductive layer and the memory cell strip comprises: forminga third mask over the second conductive layer, the third mask having apattern of the word line portion; forming a fourth mask over the secondconductive layer, the fourth mask having a pattern of the word line padportion; and etching the second conductive layer and the memory cellstrip using the third mask and the fourth mask as a second combinedetching mask.